First I want to say I am an absolute beginner to this and though I've tried to do some research about it, I wasn't able to take away anything useful.
I want to install Ubuntu onto my Samsung t7 500gb external SSD while also using it as the 'live USB installation media'. I also would like to split the SSD into parts so that I can use a part of it to store files for my Windows OS but that's optional, the priority is to get Ubuntu running on the external SSD without messing with Windows installed on the internal SSD in my laptop. I can't use a pen drive now to create a live USB installer which I can use to install onto the external SSD, that's why I'm trying to use the SSD as the live installer.
I've seen answers suggesting to use Unetbootin to use the internal hard drive as the installation media but I would very much prefer to leave the SSD with Windows installed in it untouched as I don't really know what I'm doing and if something goes wrong I don't want it to screw up my Windows installation. My idea is to split the external SSD into 3 parts (if that's possible); a part which serves as the live USB installation, a part which I can install Ubuntu on, and a part which I can use to store other files as I won't be using all 500gb for Ubuntu. Most guides seem to do something called "shrink volume" in device manager to create unallocated space for installing Ubuntu but that option seems to be greyed out in the external SSD.
Any help is appreciated.